Apoptosis is an active process whereby selected cells undergo drastic morphological changes. (Kerr et al., 1972, Br. J. Cancer, 26:239-245.) The goal of apoptosis is to attain an orderly disintegration of cells into structures suitable for phagocytosis. (Duval et al., 1985, Immunology, 56:351-358; Savill et al., 1989, J. Clin. Invest., 83:865-875; and Savill et al., 1989, J. Clin. Invest., 84:1518-1527.) The orderly disintegration of cells includes chromatin condensation and degradation of genomic DNA into nucleosomal fragments and cellular fission to form apoptotic bodies. The precise molecular mechanism of apoptosis is uncharacterized.
Apoptosis is known to be involved in developmental and tissue specific processes which require removal of cell populations. (Hamburger et al., 1982, Neurosci. Comment., 1:39-44 and Lesser et al. Biochimica et Biophysica Acta, 308:426-437.) Apoptosis is also known to be involved in the immunological process of cell selection. (Teh et al., 1988, Nature, 335:229-233; Shi et al., 1989, Nature, 339:625-626; and Nunz et al., 1991, Nature, 353:71-74.) The colonic mucosa is known to undergo apoptosis as a result of an invasion by Shigella (Zychlinsky et al., 1992, Nature, 358: 167-169.) During HIV infection, virally induced T cell death has been shown to follow an apoptotic pathway. (Terai et al., 1991, J. Clin. Invest., 87:1710-1715). Similarly, during tumor regression, tumor cell death has been shown to follow an apoptotic pathway. (Szende et al., 1990, Cancer Research, 50:3716-3721; Trauth et al., 1989, Science, 243:301-304; and Kyprianou et al., 1991, Cancer Res., 52:162-166.)
Control of apoptosis has been shown to be useful with respect to specific cells having crucial relevance to developmental biology. (Ellis et al., 1991, Annu. Rev. Cell. Biol., 7:663-398 and Raff, 1992, Nature, 356:397-400). Additionally, it would be useful to control apoptosis with respect to treatments involving viral and bacterial pathogens. (Meyaard et al., 1992, Science, 257:217-220 and Zychlinsky et al., supra.) Cancer chemotherapy could also be enhanced by the controlling apoptotic pathways. (Wyllie et al., 1985, Anticancer Res., 5:131-136.)
The chemical induction of apoptosis is target cell dependent. Glucocorticoids, such as dexamethasone, have been shown to induce apoptosis in thymocytes. (Telford et al., 1991, Cell Prolif., 24: 447.) Cycloheximide, a known inhibitor of protein synthesis and actinomycin D, a known inhibitor of mRNA transcription, have also been shown to be powerful inducers of apoptosis in many cell lines, including Molt-4. (Bansal et al., 1991, FASEB J., 5:211-216; Waring et al., 1990, J. Biol. Chem., 265:14476-14482; Uesawa et al., 1991, Biochemistry, 30:9242-9246; and Dedon et al., 1992, Biochemistry, 31:1909-1917.) Other inducers of apoptosis include UV irradiation, camptothecin, aphidocholin, cisplatin, vincristine, and phorbol myristate acetate plus ionomycin. (Cotter et al. 1992, Cancer Research, 52:9979-1005.)
The inhibition of apoptosis is also target cell dependent. In addition to being classified as apoptosis inducers, actinomycin D and cyloheximide have also been classified as powerful inhibitors of apoptosis in many cell lines, including Molt-4. (Telford, supra.) Other apoptosis inhibitors include various endonuclease inhibitors, e.g. Zn.sup.2+ (Cohen et al., 1984, J. Immunol., 132:38-42 and Duke et al., 1983, Proc. Natl. Acad. Sci., U.S.A., 80:6361-6365) and aurintricarboxylic acid. (Telford, supra)
Inhibition of apoptotic deletion of autoreactive T-cell clones may be achieved by treatment with immunosuppressant cyclosporin A. In this case, the inhibition of apoptosis may lead to autoimmune disease. Other special inhibitors of apoptosis, including various steroids and interleukins, are reviewed by Ellis et al., 1991, Annu. Rev. Cell. Biol., 7:663-398.
The latter stage of apoptosis, i.e. the induction of fission events leading to the formation of apoptosis bodies, may be inhibited by the use of microfilament-disrupting agents such as cytochalasin B and staurosporin. (Cotter et al., 1992, Cancer Res., 52:997-1005.)
Agents which inhibit the expression of the oncogene cMyc (Shi et al., 1992, Science, 257:212-215) or which cause the over expression of proto-oncogene bcl-2 (Jacobson et al., 1993, Nature, 361:365-369) can inhibit the induction of apoptosis.
What was needed was a method for inducing apoptosis which employs a chemically reactive compound specifically activatable for inducing apoptosis by binding target cells. What was also needed was an inhibitor of such specific chemically reactive inducers of apoptosis.